The introduction of monoclonal antibodies has heralded a new era in treating chronic lymphocytic leukemia (CLL); Rituximab has moved into frontline CLL drug combinations, and Campath-1H has been approved for salvage therapy. Our group has been actively pursuing the pre-clinical and clinical development of a humanized HLA-DR beta-chain antibody, Hu1D10. Our preliminary studies have demonstrated that Hu1D10 induces apoptosis in a caspase-independent pathway involving generation of reactive oxygen species, release of apoptosis-inducing factor, and activation of ly/syk. While our data support the importance of HLA-DR signaling in the apoptotic effect of this therapy, AKT is also activated by this therapy. Furthermore, combination of Hu1D10 with inhibitors of PI3 kinase results in synergistic apoptosis. These findings suggest that dual survival and death signals are being generated by Hu1D10 therapy. Concurrent with these investigations, we have nearly completed a phase I trial with pharmacokinetic studies suggesting that the rate of clearance of Hu1D10 is directly proportional to 1D10 antigen on the CLL cells. If this observation is confirmed, it might be possible to dose Hu1D10 based upon pre-treatment density of tumor 1D10 antigen expression. In addition, we have seen clinical activity in resistant CLL possessing a del(17p13.1) chromosomal abnormality. Based upon these promising data, continued development of Hu1D10 and other pan HLA-DR antibodies is planned. This proposal seeks support of a multi-modality effort to perform detailed clinical and laboratory investigation of Hu1D10 in CLL. Our four aims are to determine 1) the clinical activity, toxicity, and pharmacology of this targeted therapy in genetically characterized CLL patients, 2) the importance of ROS generation, signal transduction, and genetic subtype to the cytotoxic effect mediated by Hu1D10, 3) properties that convey resistance to Hu1D10 in CLL, and 4) the most promising combination strategies with Hu1D10 for future phase I trials. Performance of these clinical and laboratory studies related to Hu1D10 in CLL by this multifaceted group will facilitate optimal and safe development of this agent and potentially other HLA-DR-directed antibodies that will soon be entering clinical trials for hematologic malignancies and solid tumors.